InvalidateEmails.cls

global class InvalidateEmails implements SandboxPostCopy {
 global void runApexClass(SandboxContext context) {
  System.debug(context.organizationId());
  System.debug(context.sandboxId());
  System.debug(context.sandboxName());

  run();
 }

 static Map < String, Map < String, Object >> objectConditionals = new Map < String, Map < String, Object >> {
  'Lead' => new Map < String,
  Object > {
   'isConverted' => false
  }
 };

 global static void run() {
  // Map from SObject to List of Email Fields
  Map < String, List < String >> soEmailFieldMap = findEmaiLFields();
  // Invalidate Email fields found on SObjects
  processEmailFields(soEmailFieldMap);
 }

 private static Map < String, List < String >> findEmaiLFields() {
  Map < String, List < String >> soEmailFieldMap = new Map < String, List < String >> ();
  // Iterate over all SObjects
  for (SObjectType soType: Schema.getGlobalDescribe().values()) {
   DescribeSObjectResult soDescribe = soType.getDescribe();
   // Skip objects we cannot query or update
   if (!soDescribe.isQueryable() || !soDescribe.isUpdateable()) continue;
   String objectTypeName = soDescribe.getName();
   // Iterate over all fields found on a given SObject
   for (SObjectField soField: soDescribe.fields.getMap().values()) {
    DescribeFieldResult field = soField.getDescribe();
    // Skip non Email type fields
    if (field.getType() != Schema.DisplayType.EMAIL) continue;
    // Skip emails that cannot be filtered on
    if (!field.isFilterable()) continue;
    // Collect all Email fields found
    if (soEmailFieldMap.containsKey(objectTypeName)) {
     soEmailFieldMap.get(objectTypeName).add(field.getName());
    } else {
     soEmailFieldMap.put(objectTypeName, new List < String > {
      field.getName()
     });
    }
   }
  }
  return soEmailFieldMap;
 }

 private static void processEmailFields(Map < String, List < String >> soEmailFieldMap) {
  // Iterate over the SObject to Email Fields collection
  for (String objectName: soEmailFieldMap.keySet()) {
   // Get any specified conditionals
   Map < String, Object > conditionals = new Map < String, Object > ();
   if (objectConditionals.containsKey(objectName)) conditionals = objectConditionals.get(objectName);
   // Build a list of all fields that need to be queried
   List < String > emailFields = soEmailFieldMap.get(objectName);
   List < String > fieldList = new List < String > ();
   fieldList.addAll(emaiLFields);
   fieldList.addAll(conditionals.keySet());
   // Generate a SOQL query to get records with non null emails
   String soql = getSOQL(objectName, fieldList);
   System.debug(soql);
   List < SObject > records = new List < SObject > ();
   // Iterate over queried SObject records
   for (SObject record: Database.query(soql)) {
    // Skip records that do not match specified conditons
    if (!checkConditions(record, conditionals)) continue;
    // Iterate over Email fields found on SObject and invalidate values
    for (String field: emailFields) {
     String email = (String) record.get(field);
     if (String.isEmpty(email)) continue;
     record.put(field, email.replaceAll('\\W', '_') + '@disabled.diabled');
    }
    records.add(record);
   }
   System.debug(JSON.serializePretty(records));
   update records;
  }
 }

 private static boolean checkConditions(SObject record, Map < String, Object > conditionals) {
  for (String field: conditionals.keySet()) {
   Object value = record.get(field);
   Object condition = conditionals.get(field);
   if (value != condition) return false;
  }
  return true;
 }

 global static String getSOQL(String objectTypeName, List < String > fieldList) {
  List < String > conditionals = new List < String > ();
  for (String field: fieldList) conditionals.add(field + ' != null');
  String soql = 'SELECT {!fieldList} FROM {!objectTypeName} WHERE {!conditionals}';
  return soql
   .replace('{!fieldList}', String.join(fieldList, ','))
   .replace('{!objectTypeName}', objectTypeName)
   .replace('{!conditionals}', String.join(conditionals, ' OR '));
 }
}